/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.convert.support;

import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;
import org.springframework.lang.Nullable;

import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

/**
 * Converts a {@link ByteBuffer} directly to and from {@code byte[] ByteBuffer} directly to and from {@code byte[]s} and indirectly
 * to any type that the {@link ConversionService} support via {@code byte[]}.
 *
 * @author Phillip Webb
 * @author Juergen Hoeller
 * @since 4.0
 */
final class ByteBufferConverter implements ConditionalGenericConverter
{

    private static final TypeDescriptor BYTE_BUFFER_TYPE = TypeDescriptor.valueOf(ByteBuffer.class);

    private static final TypeDescriptor BYTE_ARRAY_TYPE = TypeDescriptor.valueOf(byte[].class);

    private static final Set<ConvertiblePair> CONVERTIBLE_PAIRS;

    static
    {
        Set<ConvertiblePair> convertiblePairs = new HashSet<>(4);
        convertiblePairs.add(new ConvertiblePair(ByteBuffer.class, byte[].class));
        convertiblePairs.add(new ConvertiblePair(byte[].class, ByteBuffer.class));
        convertiblePairs.add(new ConvertiblePair(ByteBuffer.class, Object.class));
        convertiblePairs.add(new ConvertiblePair(Object.class, ByteBuffer.class));
        CONVERTIBLE_PAIRS = Collections.unmodifiableSet(convertiblePairs);
    }


    private final ConversionService conversionService;


    public ByteBufferConverter(ConversionService conversionService)
    {
        this.conversionService = conversionService;
    }


    @Override
    public Set<ConvertiblePair> getConvertibleTypes()
    {
        return CONVERTIBLE_PAIRS;
    }

    @Override
    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType)
    {
        boolean byteBufferTarget = targetType.isAssignableTo(BYTE_BUFFER_TYPE);
        if (sourceType.isAssignableTo(BYTE_BUFFER_TYPE))
        {
            return (byteBufferTarget || matchesFromByteBuffer(targetType));
        }
        return (byteBufferTarget && matchesToByteBuffer(sourceType));
    }

    private boolean matchesFromByteBuffer(TypeDescriptor targetType)
    {
        return (targetType.isAssignableTo(BYTE_ARRAY_TYPE) || this.conversionService.canConvert(BYTE_ARRAY_TYPE, targetType));
    }

    private boolean matchesToByteBuffer(TypeDescriptor sourceType)
    {
        return (sourceType.isAssignableTo(BYTE_ARRAY_TYPE) || this.conversionService.canConvert(sourceType, BYTE_ARRAY_TYPE));
    }

    @Override
    @Nullable
    public Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType)
    {
        boolean byteBufferTarget = targetType.isAssignableTo(BYTE_BUFFER_TYPE);
        if (source instanceof ByteBuffer)
        {
            ByteBuffer buffer = (ByteBuffer) source;
            return (byteBufferTarget ? buffer.duplicate() : convertFromByteBuffer(buffer, targetType));
        }
        if (byteBufferTarget)
        {
            return convertToByteBuffer(source, sourceType);
        }
        // Should not happen
        throw new IllegalStateException("Unexpected source/target types");
    }

    @Nullable
    private Object convertFromByteBuffer(ByteBuffer source, TypeDescriptor targetType)
    {
        byte[] bytes = new byte[source.remaining()];
        source.get(bytes);

        if (targetType.isAssignableTo(BYTE_ARRAY_TYPE))
        {
            return bytes;
        }
        return this.conversionService.convert(bytes, BYTE_ARRAY_TYPE, targetType);
    }

    private Object convertToByteBuffer(@Nullable Object source, TypeDescriptor sourceType)
    {
        byte[] bytes = (byte[]) (source instanceof byte[] ? source : this.conversionService.convert(source, sourceType, BYTE_ARRAY_TYPE));

        if (bytes == null)
        {
            return ByteBuffer.wrap(new byte[0]);
        }

        ByteBuffer byteBuffer = ByteBuffer.allocate(bytes.length);
        byteBuffer.put(bytes);

        // Extra cast necessary for compiling on JDK 9 plus running on JDK 8, since
        // otherwise the overridden ByteBuffer-returning rewind method would be chosen
        // which isn't available on JDK 8.
        return ((Buffer) byteBuffer).rewind();
    }

}
